With the rapid development of Broadband Wireless Access (BWA) technology, the technology for broadband metropolitan area access using wireless resources finds a strong vitality and a broad market space. At the same time, wireless spectrum resources are very precious. Especially for some areas that are not well planned or some license-exempt frequency bands, a plurality of Base Stations (BS) usually runs on the same channel. As a result, the systems which home to these BSs may interfere with each other. Therefore, for the coexistence of devices under the same frequency band, especially the coexistence of devices under license-exempt frequency bands, some coexistence mechanisms among devices needs to be established.
It should be noted that Neighbor BSs in the context refer to Base Stations that have a common coverage area in which one or more effective terminals exist. As shown in FIG. 1, BS1 and BS2 are near to each other geographically and lie in each other's coverage area, respectively, but because there is not any effective terminal in the common coverage area of stations BS1 and BS2 and the wireless networks of two parties do not interfered severely with each other, stations BS1 and BS2 are not referred to as Neighbor BSs. However, although the overlap area between BS2 and BS3 is small and both do not lie in each other's coverage area, there are effective terminals in the overlapped coverage area and the wireless networks of two parties interfere with each other, so BS2 and BS3 are referred to as Neighbor BSs.
In a coexistence system, it is usually required that the frame timing for transmitting and receiving a signal among BSs should be aligned rigidly so that BSs that are near to each other geographically would not interfere with each other on signals receiving and transmitting. For example, for BS1 and BS2 shown in FIG. 1, if BS2 is receiving a signal when BS1 is transmitting a signal, BS1 will interfere with BS2 on receiving signals from its subordinate terminals. Therefore, receiving/transmitting synchronization must be guaranteed among BSs.
The negotiation between Neighbor BSs is very important in solving the problem of coexistence. When air interface resources are allocated, the BS sends data to a terminals in an interference-free area using competitive air interface resource (such as time period, subchannel, etc), and sends data to a terminal in an interfered area using dedicated air interface resource (such as time period and sub channel).
An operating BS needs to know the interference state of a terminal all the time, and needs to know whether each terminal is interfered with and from which base stations the interference came. Moreover, when a new Neighbor BS nearby is started, the operating BS updates the interference information of the terminal.
As shown in FIG. 2, in the case that a BS near the coexistence BS is started up, during the initialization process for the SBS/IBS (wherein SBS refers to Startup Base Station, and IBS refers to Initializing Base Station), a WBS/OBS (wherein WBS refers to Working Base Station, and OBS refers to Operating Base Station) collects and notifies the SBS/IBS of information of interference state in which the SBS/IBS interferes with the local network. Specifically, the procedure includes the following steps.
1) An IBS broadcasts necessary information, such as IP address, to terminals of the neighboring network in the coverage area (such as SS_A, etc.) by sending an IPBC (IP Address Broadcast) message via an air interface.
2) In response to receiving this message, each terminal that received the message via the air interface carries the information contained in the received message and information containing the identity and state of the terminal in an interference report message via the air interface, and sends the interference report message to the OBS to which the terminal homes.
3) The OBS collects the information reported by each terminal, and updates a local coexistence information DB (Database) with the related information.
4) In response to updating the local coexistence information DB, the OBS sends, via a wired network, its contact information, identification, and the related information in the coexistence information DB to the IBS according to the IP address information of the IBS.
5) In response to receiving the information from the OBS via the wired network, the IBS obtains related information and updates its coexistence information DB;
6) The IBS obtains the IP address of the OBS from the message sent by the OBS and responds to the OBS according to the IP address, carrying other information of the IBS in the response message;
7) The OBS updates the DB according to the above other information carried in the message sent from the IBS, and then goes on with the subsequent processes.
According to the interference source information reported from all the terminals, the OBS may establish coexistence DB information which includes information of the Neighbor BS and information of the subordinate terminal. One example of the information of the coexistence DB is as shown in Table 1 and Table 2:
TABLE 1List of information of the Neighbor BS in a coexistence DBBS IndexIP addressOther Information1XXX.XXX.XXX.XXX......2XXX.XXX.XXX.XXX........................
TABLE 2List of information of the subordinate terminal in a coexistence DBNumber ofTerminalinterferencenumbersources thatInterferenceInterference(such ashave beensource 1Interferencesource 2InterferenceOther statebasic CID)found(Index)strength(Index)strength... ...information12....................................21....................................................................................
The IBS in initialization state sends a broadcast message to the terminals belonging to the Neighbor BS in the coverage area via an air interface. The broadcast message includes the contact information of the IBS, such as IP address information or other information. The contact information must correspond to an IBS uniquely. As shown in FIG. 3, the broadcast message is sent frame by frame. The format of a frame includes SOF (Start of Frame), Payload, CRC (Cyclic Redundancy Check) and EOF (End of Frame), in which the Payload usually carries IP address information of the transmission BS, and the CRC is used for checking the integrity and correctness of a message. Taking a 32-bit address for IPv4 for example, the package may employ the format of SOF+32 bit IP Address+8 bit CRC+EOF.
A complete broadcast message may be sent in segments according to physical frame format, and only a part of the message is sent in each physical frame that meets the requirements. For example, as shown in FIG. 4, a block of a message is sent in every N frames starting from frame M, and totally n frames are sent. The n frames form a complete broadcast message frame. Terminals of the “same batch” in the coverage area of an IBS receive the above broadcast message frame simultaneously.
When a plurality of terminals exists in a common coverage area belonging to both of an IBS and an OBS, a part of the terminals that receive the broadcast signal may not be able to correctly receive a complete broadcast message due to the interference from other signals or other reasons. Therefore, the terminals may not correctly report the received message to the OBS to which they home. As a result, the OBS may not obtain and record the information of terminals the IBS interfered with.